1) Field of the Invention
The present invention relates to an optical switch applied to a wavelength division multiplexing (WDM) system, and particularly to an optical switch (wavelength selective switch) which comprises a plurality of input/output ports (may comprise a single input or output port) and has a function capable of selectively outputting an input wavelength-multiplexed signal to any output port for each wavelength.
2) Description of the Related Art
FIG. 13 is a top schematic view showing a conventional optical switch 102A (refer to U.S. Pat. No. 6,707,959). The optical switch 102A shown in FIG. 13 comprises an input/output unit 122, a concave mirror 120, a diffraction grating 124 arranged in Ebert type and a MEMS (Micro Electro Mechanical Systems) mirror array 126. The input/output unit 122 is constituted of a plurality of optical fibers 132 (in this case, four optical fibers 132A to 132D) a plurality of collimate lenses (in this case, four collimate lenses 134A to 134D) and a lens 136 as shown in FIG. 14, for example.
In the optical switch 102A constituted in this manner, a wavelength-multiplexed light beam from any one of the optical fibers 132 (for example, a light beam from the optical fiber 132A) is spectrally diffracted to be subjected to switching of an output path for each wavelength, and is output to any one of the optical fibers 132B to 132D, for example. In other words, the optical switch 102A can perform a wavelength selecting operation which is an operation of selecting a wavelength to be output to the output fiber 132B to 132D as an output destination.
For example, after a light beam is made to be a parallel beam in the collimate lens 134A corresponding to the optical fiber 132A and the direction thereof is changed in the lens 136, the parallel beam is reflected on the concave mirror 120 to be directed to the diffraction grating 124, and it is separated for each wavelength in the diffraction grating 124 and then is reflected on the concave mirror 120 again to be directed to the MEMS mirror array 126.
The MEMS mirror array 126 comprises MEMS mirrors (not shown) for individually reflecting a light beam separated for each wavelength, and controls an angle of each MEMS mirror in a direction perpendicular to the sheet (that is, in an arrangement direction of the optical fibers 132A to 132D), thereby controlling a reflecting direction of the light beam for each wavelength. A light reflected on the MEMS mirror reversely travels on the path and is classified to any one of the fibers 132B to 132D in correspondence to the angle of the light beam for each wavelength incident into the input/output unit 122. Thus the wavelength selecting operation is enabled.
Additionally, a well-known technique related to the present invention includes a wavelength router 210 shown in FIG. 15 (refer to U.S. Pat. No. 6,439,728). FIG. 16 is a diagram viewed from an arrow A in FIG. 15 and shows an arrangement relationship between the optical fibers 212, 215 and reverse reflectors 230 (1 . . . N) provided in the wavelength router 210.
The input fiber 212 and the output fibers 215 shown in FIG. 15 correspond to the input/output unit 122 in FIG. 13 and the reverse reflectors 231 (1 . . . N) correspond to the MEMS mirror array 126. As shown in FIG. 16, the arrangement relationship between these input fiber 212, the output fibers 215 and the reverse reflectors 230(1 . . . N) is also similar. In other words, the reverse reflectors 230 (1 . . . N) in FIG. 15 are arranged in parallel in a direction parallel to the sheet, and the input fiber 212 and the output fibers 215 are arranged in parallel in a direction perpendicular to the sheet.
In the wavelength router 210 constituted in this manner, a light beam 218 output from the input fiber 212 propagates through a glass body 211, is reflected on a concave mirror 240 constituting the inner wall of the glass body 211, and is spectrally diffracted in a diffraction grating 225, and then is reflected on the concave mirror 240 again and directs toward the reverse reflectors 230 (1 . . . N) for each wavelength. When reflecting a spectrally-diffracted light beam, each reverse reflector 230 (1 . . . N) moves an optical axis of the reflected light in parallel to a direction 235 corresponding to the arrangement direction of the optical fibers 215. Thus, the reflected light beam can be coupled with the optical fiber 215 (1 . . . M) as an output destination via re-reflection in the concave mirror 240 and the diffraction grating 225.
FIG. 17 shows a structure example of each reverse reflector 230 (1 . . . N). Each of the reverse reflectors 230 (1 . . . N) can have a structure denoted with numeral 230e in FIG. 17. The reverse reflector 230e comprises a prism 269 and two MEMS mirror arrays 262 and 263 directly contacted on the right-angle faces of the prism 269. In the MEMS mirror array 263, M MEMS mirrors 266 (1 . . . M) for coupling a reflected light to the optical fiber 215 (1 . . . M) as the output destination are arranged, and the MEMS mirrors 265 in the MEMS mirror array 262 are controlled an inclination angle thereof in order to reflect a light beam from the concave mirror 240 on any one of the MEMS mirrors 266 (1 . . . M).
However, there is a problem that the size of the optical switch 102A described in U.S. Pat. No. 6,707,959 is relatively large.
Specifically, when being spectrally diffracted, a wavelength-multiplexed light beam input into the diffraction grating 124 is output in a direction different from the incident direction of the wavelength-multiplexed light beam, that is, in a direction different from the input light beam about the axis 120A of the concave mirror 120. Therefore, the MEMS mirror array 126 for switching the reflecting direction of a light beam for each wavelength requires to be provided at the opposite side to the input/output unit 122 about the diffraction grating 124. As a result, it is necessary to provide a relatively large space totally for arranging the optical members 122, 120, 124 and 126 constituting the optical switch 102A, and thus the size of the optical switch 102A is accordingly large.
On the contrary, in the wavelength router 210 described in U.S. Pat. No. 6,439,728, when being spectrally diffracted, a wavelength-multiplexed light beam input into the diffraction grating 225 can be reflected in a direction substantially identical to the incident direction of the wavelength-multiplexed light beam. Thus, though the reverse reflector 230 corresponding to the MEMS mirror array 126 shown in FIG. 13 can be provided at the same side as the optical fibers 212 and 215 corresponding to the input/output unit 122 and the diffraction grating 225. However since the number of MEMS mirrors required in each reverse reflector 230 increases, the structure becomes complicated and the size of the member itself also becomes larger, thereby causing a problem in down-sizing or causing interference of the arrangement position between the optical fibers 212 and 215 and the reverse reflectors 230.